The present invention relates to a method for determining an adjustment parameter for a hydraulic actuator arrangement in a motor vehicle drivetrain, wherein the actuator arrangement has a pump and a hydraulic cylinder and a pressure port of the pump is connected to a port of the hydraulic cylinder, wherein the adjustment parameter is a function of the volume of the fluid that must be delivered by the pump in order to realize a predetermined operating point of the actuator arrangement, wherein the operating point is defined by a value pair of an operating point rotational speed value of the pump and an operating point control value of the pump.
The present invention also relates to a method for actuating a friction clutch of a motor vehicle drivetrain by means of a hydraulic actuator arrangement of the type mentioned in the introduction, wherein the friction clutch is coupled to a piston of the hydraulic cylinder, and wherein an operating point of the actuator arrangement corresponds to an operating point of the friction clutch.
Hydraulic actuators of said type are used in particular for the automatic engagement of gears in automated transmissions for motor vehicles, or for the automatic actuation of clutches within a drivetrain of a motor vehicle. Here, the elements to be actuated generally have certain operating points at which, for example, a gear is engaged or a clutch begins to transmit a first torque. Here, adjustment to said operating points must be performed, and said operating points must be set, as quickly and precisely as possible by means of the actuators.
Owing to wear and abrasion, said operating points are however constantly subject to changes, which must often be compensated already during operation in order to permit efficient and comfortable operation. External conditions, for example as a result of temperature changes, also have an influence on the present operating point of an element to be actuated. Here, this relates not only to the elements to be actuated but also to the actuator arrangements themselves. The actuators to be controlled must consequently be continuously adapted to the changed operating points during ongoing operation.
One very important operating point in a motor vehicle drivetrain is, for example, the engagement point of the friction clutch which connects the drive to the transmission and which, in an automated drivetrain, is actuated by means of an actuator arrangement mentioned in the introduction. In technical parlance, this operating point is often referred to as the biting or kiss point, and the corresponding method for determining said point is referred to as biting or kiss point adaptation. Here, the biting point is defined as the point at which the closing friction clutch transmits a first, low torque in the range of less than 10 Nm. To permit smooth and comfortable clutch engagement, it is necessary, in the case of an automated transmission, for said point to be determined as accurately as possible and to subsequently be set as precisely as possible by the actuator arrangement. A method for biting point adaptation is known for example from DE 196 52 244 A1.
A further method for determining the operating point of an automatically actuated friction clutch is disclosed in DE 102 44 393 A1. Here, in the actuator performing the actuation, the different pressure profiles are measured at a hydraulic cylinder, and the operating point is determined on the basis of the characteristic curve thus recorded. For this purpose, the actuator arrangement has various pressure sensors that are evaluated by means of a control unit.
DE 10 2007 057 081 B4 presents a further biting point adaptation method in which, to determine the biting point, use is made of rotational speed measurements at the corresponding shafts in the drivetrain. Here, a measurement of the pressure in the actuators that perform the actuation is not necessary.
U.S. Pat. No. 5,853,076 describes a method with which an actuator arrangement can be continuously readjusted in accordance with the adaptation methods described above. Here, the method utilizes the fact that pressure sensors are already provided in the actuator arrangement for the biting point adaptation, by means of which pressure sensors it is possible to measure the pressure profiles in the hydraulic cylinders that actuate the clutch. The actuator arrangement can be readjusted on the basis of the measurement values thus obtained.
A disadvantage of the known adjustment methods for hydraulic actuator arrangements is however that they are regulated as a function of the pressure conditions at the hydraulic cylinder, and thus always require the measurement of the pressure at the cylinder. This inevitably requires additional pressure sensors within the actuator arrangements, which pressure sensors are however no longer required in the case of some biting point adaptation methods.